Dual clutch automatic transaxle

ABSTRACT

A multiple speed transaxle includes first and second input shafts, first and second output shafts, a layshaft, an idler shaft, a first set of selectable torque paths between the first input shaft and first output shaft, a second set of selectable torque paths between the second input shaft and the second output shaft, the second set including the layshaft and idler shaft, and a selectable torque path between the first input shaft and second output shaft including the layshaft and idler shaft.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of the co-pending U.S. patentapplication Ser. No. 10/853,094, filed May 25, 2004.

BACKGROUND OF THE INVENTION

This invention relates to automatic transmissions having a layshaftkinematic arrangement, particularly to automatic transaxles having dualinput clutches, but no torque converter.

Automatic transmissions for transmitting power between an input and anoutput, either over a continuously variable range of speed ratios or indiscrete step changes among speed ratios, have associated with themseveral sources of parasitic losses, which adversely affect fueleconomy. These losses are associated with a torque converter, openhydraulic friction clutches and brakes, hydraulic pump, and gear meshes.

To improve fuel economy in a motor vehicle having an automatictransmission, an automated shift manual (ASM) transmission can be usedto eliminate or substantially reduce all of these parasitic lossesexcept gear mesh losses. An ASM transmission generally performs gearratio changes by first interrupting torque transmitted from the engineto the transmission input, preparing the transmission componentsassociated with the next speed ratio, and then restoring torque at theinput. A primary functional feature of ASM transmissions is the need tointerrupt power transmitted from the engine to the transmission inputshaft before or during each gear ratio change.

Dual clutch layshaft transmissions are essentially two ASMtransmissions, one providing odd numbered gears and one providing evennumbered gears. Shifts between odd numbered gears and even numberedgears can be accomplished without interrupting power flow. Whileoperating in an odd numbered gear, couplers can be actuated to configurethe transmission for the next even numbered gear. Dual clutchtransmissions have parasitic losses only slightly higher than ASMtransmissions.

Motor vehicles, in which the front wheels are the driven wheels and theengine and transmission are located in a forward engine compartment,generally require the engine and transmission to be arranged in a spacewhose lateral dimension is limited by the spacing between the frontwheels. The engine compartments of such vehicles are both narrow andshort. When the engine is also of the type having six in-line cylinders,there is an acute need to minimize the package space occupied by thetransaxle, particularly its lateral dimension, in order to conservespace for long engines.

SUMMARY OF THE INVENTION

A transaxle according to this invention is a layshaft transaxle havingdual friction clutches and two final drive pinions. The sixth forwarddrive gear is located on an idler shaft, which transmits torque to anoutput shaft associated with particular gear ratios, e.g., odd-numberedgear ratios. A driving gear for the fifth gear ratio is also an idlergear for the sixth gear ratio. Producing the sixth gear in this wayallows a substantial reduction in length of the transaxle.

It is an advantage of this invention that the axial dimension of thetransaxle, its lateral dimensions when installed in the vehicle, isreduced sufficiently to accommodate an I6 engine in the enginecompartment. It is another advantage that its longitudinal dimension, asinstalled, provides sufficient space for V6 engines in the enginecompartment.

A multiple speed transaxle according to this invention includes firstand second input shafts, first and second output shafts, a layshaft, anidler shaft, a first set of selectable torque paths between the firstinput shaft and first output shaft, a second set of selectable torquepaths between the second input shaft and the second output shaft, thesecond set including the layshaft and idler shaft, and a selectabletorque path between the first input shaft and second output shaft, thetorque path including the layshaft and the idler shaft.

Various objects and advantages of this invention will become apparent tothose skilled in the art from the following detailed description of thepreferred embodiment, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an end view of a transmissionaccording to the present invention;

FIG. 2 is a cross section taken at planes 2—2 of FIG. 1 showing thekinematic gear arrangement of a transmission having six forward speeds;

FIG. 3 is a chart containing a preferred number of teeth for each of thegears and pinions of the transmission of FIG. 2;

FIG. 4 is a chart containing the torque ratios between the input andoutput and steps between the torque ratios for each of the forwardspeeds and reverse drive of the transmission of FIG. 2, the gears andpinions having the number of teeth shown in FIG. 3.

FIG. 5 is a cross section taken at planes 2—2 of FIG. 1 showing thekinematic gear arrangement of a transmission having seven forwardspeeds;

FIG. 6 is a chart containing a preferred number of teeth for each of thegears and pinions of the transmission of FIG. 5; and

FIG. 7 is a chart containing the torque ratios between the input andoutput and steps between the torque ratios for each of the forwardspeeds and reverse drive of the transmission of FIG. 5, the gears andpinions having the number of teeth shown in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1 and 2, a transmission according to the presentinvention includes an input 10 for driveably connecting a power source,such as an internal combustion engine or electric motor, to thetransmission, and an output 12 for driving a load, such as the drivenwheels of a motor vehicle, through a powertrain that may include a driveshaft, differential mechanism, and axle shafts. A first friction clutch14, consisting of a clutch housing and a clutch disc, alternatelyconnects and disconnects a first input shaft 16 as clutch 14 is engagedand disengaged, respectively. A second friction clutch 18, consisting ofa clutch housing and a clutch disc, connects and disconnects a secondinput shaft 20 as clutch 18 is engaged and disengaged, respectively.

A first output shaft 22 supports a first output pinion 24, which issecured to shaft 22 in continuous meshing engagement with an output gear25, secured to output 12. A second output shaft 26 supports a secondoutput pinion 28, which is secured to the shaft in continuous meshingengagement with output gear 25. An idler shaft 30 and layshaft 32 arearranged substantially parallel to the other shafts 16, 20 22 and 26.

First pairs of mutually engaged pinions and gears include a pinion 34,secured to input shaft 16 and engaged with gear 36, which is supportedon shaft 22 for rotation relative to shaft 22. A pinion 38, secured toinput shaft 16, is engaged with gear 40 and with gear 42, which issecured to idler shaft 30. Gear 40 is supported on shaft 22 for rotationrelative thereto. A pinion 44, secured to input shaft 20, is engagedwith idler gear 46, which is supported on idler shaft 30 for rotationrelative to shaft 30 and is engaged with gear 48, which is secured tolayshaft 32.

A pinion 50, which is supported on idler shaft 30 for rotation relativeto shaft 30, is engaged with gear 52, which is supported on layshaft 32for rotation relative to shaft 32.

Second pairs of mutually engaged pinions and gears include gear 52,engaged with gear 54, which is secured to output shaft 26. A pinion 56,which is supported on layshaft 32 for rotation relative to shaft 32, isengaged with gear 58, which is secured to output shaft 26. A pinion 60,secured to layshaft 32, is engaged with gear 62, which is supported onoutput shaft 26 for rotation relative to shaft 26. A reverse output gear64 is supported on output shaft 26 for rotation relative to shaft 26.

A reverse idler gear (not shown) is continually meshing with pinion 60and reverse output gear 64, thereby providing an additional mesh so thatthe direction of rotation of gear 64 is opposite the direction ofrotation of the other output gears 36, 40, 54, 58, 62 when reverse driveis selected.

Couplers 70, 72, 74 and 76 are preferably synchronizers of the type usedin automotive manual transmissions to connect a gear or pinion to ashaft, after synchronizing the speed of the shaft and that of the pinionor gear. Each coupler also disconnects the shaft and the associatedpinion or gear. An example of such a synchronizer is disclosed in U.S.Pat. No. 4,222,281. Alternatively, each coupler may be a toothed clutchhaving dogteeth that are engaged with clutch teeth on a gear or pinion.This invention may use couplers in any combination of synchronizers anddog clutches. Each coupler is secured by a hub to a shaft. For example,coupler 70 is secured by hub 78 to output shaft 22 for rotation withoutput shaft 22.

In the case where a coupler is a synchronizer, it is provided with aconical surface 80 on a blocker ring, located adjacent the hub 78 andsupported for axial displacement. The conical surface on each blockerring engages with a corresponding conical surface 82 located on a gear36, 40 located adjacent the blocker ring. Each synchronizer includes asleeve 84, supported on the hub 78 for axial displacement leftward andrightward from the positions shown in FIG. 2. When the sleeve 84 isdisplaced axially causing the synchronizer 70 to engage either of itsadjacent gears 36, 40, the conical surface 80 on a blocker ring isforced into frictional contact with a conical surface 82 on the gear.This frictional engagement synchronizes the speed of the gear with thatof the shaft 22. When the rotational speeds of the shaft and gear aresynchronized, further axial displacement of the sleeve 84 causes dogteeth on the radially inner surface of the sleeve to engage dog teethcarried on the adjacent gear. When the dog teeth of the sleeve engagethose of the gear, the shaft 22 is driveably connected to the gear.

In the case where a coupler is a dog clutch, displacement of the sleeve84 in opposite axial directions causes mutual engagement of dog teethformed on the sleeve with dog teeth carried on the gear, such that adrive connection is made between the shaft and the gear, but withoutfirst synchronizing the rotational speed of the shaft with the speed ofthe gear.

In FIG. 2, the couplers 70–76 are shown in a neutral position, betweenthe left-hand and right-hand extremities of travel of the connectingsleeve, whose engagement with dog teeth carried on the gear completesthe drive connection to the shaft. The hubs of couplers 70, 76 arerotatably secured to output shafts 22 and 26, respectively; the hub ofcoupler 72 is rotatably secured to idler shaft 30; the hub of coupler 74is secured to layshaft 32.

Coupler 70, located between gears 36, 40, releasably connectsalternately those gears to output shaft 22, and coupler 70 may bedisengaged from both gears 36, 40. Coupler 74, located between gears 52,56, releasably connects alternately those gears to layshaft 32, andcoupler 74 disengages those gears from shaft 32. Coupler 76, locatedbetween gears 62, 64, releasably connects alternately those gears tosecond output shaft 26, and coupler 76 disengages those gears from shaft26. Coupler 72, located between gears 50, 42, releasably connects anddisconnects only gear 50 and idler shaft 30.

To produce the first forward speed, clutch 18 is engaged, and theselector sleeve of coupler 76 is displaced leftward to connect gear 62and output shaft 26 mutually. Input 10 is driveably connected to shaft20 through clutch 18, causing pinion 44 to drive gear 48 and layshaft 32through idler gear 46. Pinion 60 drives gear 62, which is driveablyconnected to output shaft 26 through coupler 76. Output pinion. 28drives output 12 due to its engagement with output gear 25.

The second forward speed results by disengaging coupler 76, sliding theselector sleeve of coupler 70 leftward to connect gear 36 to outputshaft 22, disengaging friction clutch 18, and engaging clutch 14. Input10 is driveably connected to input shaft 16 through clutch 14, causingpinion 34 to drive gear 36, which drives output shaft 22 through coupler70. Output pinion 24 drives output 12 due to its engagement with outputgear 25.

The third forward speed results by disengaging coupler 70, sliding theselector sleeve of coupler 74 rightward to connect pinion 56 to layshaft32, disengaging friction clutch 14, and engaging clutch 18. Input 10 isdriveably connected to input shaft 20 through clutch 18, causing pinion44 to drive gear 48 and layshaft 32 through idler gear 46. Gear 48drives layshaft 32 and pinion 56 through coupler 74. Pinion 56 drivesgear 58 and output shaft 26. Output pinion 28 drives output 12 due toits engagement with output gear 25.

The fourth speed results by disengaging coupler 74, sliding the selectorsleeve of coupler 70 rightward to connect gear 40 to output shaft 22,disengaging friction clutch 18, and engaging clutch 14. Input 10 isdriveably connected to input shaft 16 through clutch 14, causing pinion38 to drive gear 40, which drives output shaft 22 through coupler 70.Output pinion 24 drives output 12 due to its engagement with output gear25.

The fifth speed results by disengaging coupler 70, sliding the selectorsleeve of coupler 74 leftward to connect pinion 52 to layshaft 32,disengaging friction clutch 14, and engaging clutch 18. Input 10 isdriveably connected to input shaft 20 through clutch 18, causing pinion44 to drive gear 48 and layshaft 32 through idler gear 46. Gear 48drives layshaft 32 and pinion 52 through coupler 74, and pinion 52drives gear 54 and output shaft 26. Output pinion 28 drives output 12due to its engagement with output gear 25.

The sixth speed results by disengaging coupler 74, sliding the selectorsleeve of coupler 72 leftward to connect pinion 50 to idler shaft 30,disengaging friction clutch 18, and engaging clutch 14. Input 10 isdriveably connected to input shaft 16 through clutch 14, causing pinion38 to drive gear 42, which drives idler shaft 30 and pinion 50 throughcoupler 72. Pinion 50 drives gear 54 through gear 52, which, for sixthgear operation, functions as an idler. Gear 54 drives output shaft 26.Output pinion 28 drives output 12 due to its engagement with output gear25.

The output 12 is driven in the reverse direction by sliding the selectorsleeve of coupler 76 rightward to connect gear 64 to output shaft 26,and engaging friction clutch 18. Input 10 is driveably connected toinput shaft 20 through clutch 18, causing pinion 44 to drive gear 48 andlayshaft 32 through idler 46. Pinion 60 is driveably connected toreverse output gear 64, which drives output shaft 26 through coupler 76.Output pinion 28 drives output 12 due to its engagement with output gear25.

Refer now to the kinematic arrangement of the seven speed transmissionof FIG. 5, which adds to the arrangement of FIG. 2 a third pinion 90secured to input shaft 16, and a second forward drive gear 92, supportedon idler shaft 30 and engaged with the pinion 90. The first forwarddrive gear 94 is supported on idler shaft 30, but it is not secured toshaft 30.

The coupler 96, which replaces coupler 72, includes a hub that issecured to forward drive pinion 98, rather than being secured to idlershaft 30. Moving the selector sleeve of coupler 96 rightward from theneutral position driveably connects pinion 98 and gear 94; moving thatsleeve leftward driveably connects pinion 98 and idler shaft 30.

The first five forward speeds and reverse drive of the transmission ofFIG. 5 are produced identically as described with reference to FIG. 2.The sixth speed results by sliding the selector sleeve of coupler 96rightward to connect pinion 98 and gear 94, disengaging clutch 18, andengaging clutch 14. Input 10 is driveably connected to input shaft 16through clutch 14, causing pinion 38 to drive gear 94, which drivespinion 98 through coupler 96. Pinion 98 drives gear 54 through gear 52,which, for sixth and seventh gear operation, functions as an idler. Gear54 drives output shaft 26. Output pinion 28 drives output 12 due to itsengagement with output gear 25.

The seventh speed results by disengaging clutch 14, sliding the selectorsleeve of coupler 96 leftward to connect pinion 98 and idler shaft 30,and re-engaging clutch 14. Input 10 is driveably connected to inputshaft 16 through clutch 14, causing pinion 90 to drive gear 92, whichdrives idler shaft 30 due to gear 92 being secured to shaft 30. Coupler96 driveably connects idler shaft 30 and pinion 98, which drives gear 54through idler gear 52. Gear 54 drives output shaft 26. Output pinion 28drives output 12 due to its engagement with output gear 25.

An upshift from sixth to seventh gear, unlike all other single stepshifts, requires a torque break, i.e., the torsional connection betweenthe input 10 and output 25 is briefly interrupted by disengaging clutch14 while the state of coupler 96 is changed. This is mitigated becausethe 6–7 upshift is never made at high throttle; instead, it usuallyoccurs as a result of the driver reducing power demand when reachingcruising speed. Downshifts inherently involve an output torquereduction, even for powershift transmissions, because some of the enginetorque must be used to increase the engine speed. Double step shifts,such as those from fifth gear to seventh gear, and from seventh gear tofifth gear can be performed without interrupting torque.

In accordance with the provisions of the patent statutes, the principleand mode of operation of this invention have been explained andillustrated in its preferred embodiment. However, it must be understoodthat this invention may be practiced otherwise than as specificallyexplained and illustrated without departing from its spirit or scope.

1. A multiple speed transaxle for motor vehicles, comprising: an input;first and second input shafts; a first clutch driveably connected to theinput and the first input shaft for driveably connecting anddisconnecting the input and the first input shaft; a second clutchdriveably connected to the input and the second input shaft fordriveably connecting and disconnecting the input and the second inputshaft; first and second output shafts; first pairs of mutually engagedpinions and gears, a pinion of each first pair secured to the firstinput shaft, a gear of each first pair being located on the first outputshaft; a first coupler for driveably connecting the first input shaftand first output shaft through a selected first pair; an idler shaft; alayshaft; a gearset including a pinion secured to the second inputshaft, an idler gear rotatably supported on the idler shaft and engagedwith said pinion, and a gear secured to the layshaft and engaged withthe idler gear; second pairs of mutually engaged pinions and gears, amember of each second pair being located on the layshaft, another memberof each second pair being located on the second output shaft; thirdpairs of mutually engaged pinions and gears, a pinion of each third pairbeing secured to the first input shaft, a gear of each third pairlocated on the idler shaft; an idler pinion supported on the idler shaftand engaged with a pinion of a second pair; a second coupler fordriveably connecting the layshaft and the second output shaft through aselected second pair; a third coupler for driveably connecting the firstinput shaft and second output shaft through a third pair, the idlerpinion and a second pair.
 2. The transaxle of claim 1, furthercomprising: a fourth coupler for driveably connecting the layshaft andthe second output shaft through a selected second pair.
 3. The transaxleof claim 1, wherein: a first pinion of a third pair is a pinion of afirst pair; a first gear of a third pair is journalled on the idlershaft and engages the first pinion of the third pair; a second pinion ofa third pair is secured to the first input shaft; a second gear of athird pair is secured to the idler shaft and engages the second pinionof a third pair; the third coupler driveably connects the first gear ofthe third pair and the idler shaft alternately to the idler pinion. 4.The transaxle of claim 1, further comprising: a first output pinionsecured to the first output shaft; a second output pinion secured to thesecond output shaft; an output; and an output gear secured to the outputfor rotation therewith, and driveably connected to the first outputpinion and the second output pinion.
 5. The transaxle of claim 1,further comprising: a pinion secured to the layshaft; and a fifth gearrotatably supported on the second output shaft and engaged with thepinion secured to the layshaft.
 6. The transaxle of claim 1, wherein:the input, the first and second input shafts, and the first and secondclutches are mutually coaxial; and the first and second output shafts,layshaft and idler shaft are mutually parallel, and parallel to a axisof the input, the first and second input shafts, and the first andsecond clutches.
 7. The transaxle of claim 1, wherein the second pairsfurther comprise: a third pinion rotatably supported on the layshaft andengaged with the idler pinion; a fourth pinion rotatably on the layshaftand spaced axially from the third pinion; a third gear secured to thesecond output shaft and engaged with the third pinion, the third pinionand third gear producing a third ratio of a speed of the layshaft and aspeed of the second output shaft; and a fourth gear secured to thesecond output shaft and engaged with the fourth pinion, the fourthpinion and fourth gear producing a fourth ratio of a speed of thelayshaft and a speed of the second output shaft.
 8. The transaxle ofclaim 7, wherein the second coupler is secured to the layshaft, islocated between the third pinion and the fourth pinion, driveablyconnects the third pinion and the fourth pinion alternately to thelayshaft, and disconnects the drive connections of the third pinion andfourth pinion to the layshaft.
 9. The transaxle of claim 1, wherein thefirst pairs further comprise: a first pinion secured to the first inputshaft; a second pinion secured to the first input shaft and spacedaxially from the first pinion; a first gear supported on the firstoutput shaft and engaged with the first pinion, the first pinion andfirst gear producing a first ratio of a speed of the first input shaftand a speed of the first output shaft; and a second gear supported onthe first output shaft and engaged with the second pinion, the secondpinion and second gear producing a second ratio of a speed of the firstinput shaft and a speed of the first output shaft.
 10. The transaxle ofclaim 9, wherein the first coupler is secured to the first output shaft,is located between the first gear and the second gear, driveablyconnects the first gear and second gear alternately to the first outputshaft, and disconnects the drive connections of the first gear andsecond gear to the first output shaft.